Firstly thank you all for replies,
So the key is to back up the private key and the address...
so I guess you have to be online for the software to check it is creating a unique wallet address no one else has then I you just go online periodically just to 'sync' up with the network and see your balance. Is that correct?
What happens if you don't go online for a month, for example? If your balance is floating around in cyberpace, is there a timelimit where it can just get lost, swamped in the ever changing, growing data?
I downloaded both electrum and bitcoin-qt to have a play with.
I was put off with electrum as I could not find any wallet addresses. It did prompt me with a seed and I could export my private address but I was unable to find any wallet addresses

Although this is a bit prejudice, I did think electrum looks a bit unprofessional in certain areas and the website doesn't look as if there is much in the way of support.
After looking at bitcoin-qt, I think I'll be more comfortable with this

although there are a few questions!!
The first question is about the being able to resize the far right column, or rather not being able to. Sods law says my wallet address doesn't quite show in the width of the column however I cannot resize it. I did take a look at github which implied it should have been fixed in the latest version but it doesn't appear to be. Any work around?
The second question is how do you back up the private key? I see there is an option to back up the wallet but I cannot see an option for the private key.
I assume the wallet balance is the total amount held within each of the wallet addresses or perhaps another way to look at it the multiple wallet addresses are just different ways to address the same wallet??
How can you delete addresses?
I'm using the latest version 0.8.3 BTW.
Once I'm synced on the network, can I 'export' the blockchain to my other computer so I don't have to download it again?
Thanks for your help guys.